Apparatuses are known for compression-moulding objects in plastics, for example caps for bottles, comprising a rotating moulding carousel that carries a plurality of moulds each comprising a die and a punch. During rotation, each die receives a dose of plastics in a highly viscous liquid state. The dose is pressed between the die and the respective punch over a circumference arc travelled by the moulding carousel. The pressing step is followed by opening of the mould and extraction of the moulded object from the apparatus.
Each dose is dispensed by an extruding device with which a transfer device is associated, which device also has the shape of a carousel, comprising a plurality of removing elements that successively remove the doses dispensed by the extruding device and transfer them to the moulding carousel.
The plastics that constitute the doses tend to adhere to the surfaces with which they come into contact, due to the physical state of the highly viscous liquid. The adhesive properties of the plastics make it difficult to transfer the dose, which can adhere to the walls of the die, especially if the dose is dropped through gravity into the die. This defect is particularly noticeable if doses of the type used to obtain preforms have to be transferred. Such doses in fact comprise a quantity of the plastics greater than the doses required to mould caps and normally have an elongated shape. The dies in which the preforms are shaped are provided with a relatively narrow and deep cavity and the dose may be unable to position itself correctly inside the die cavity because it adheres to the walls of the cavity before reaching the bottom thereof. This produces unequal distribution of the plastics in the cavity, which may cause defects in the preform and therefore in the bottle.
Furthermore, a portion of dose may even remain outside the cavity of the die, protruding therefrom and preventing the die and the punch from pressing against each other during the moulding phase. This may cause not only the production of rejects and an arrest of the production cycle to clean the reject material off the mould but also possible damage to the mould and to its driving device.
Known apparatuses are thus not suitable for processing doses of relatively large dimensions such as for example the doses for obtaining preforms for bottles.